The present invention relates to a nickel plating solution to which a salt of an element in Group IIa in the periodic table is added, a method of copper-nickel-chromium or nickel-chromium bright electroplating and a film obtained by such a plating method. The nickel plating film is a bright electroplating film having excellent corrosion resistance.
Copper-nickel-chromium plating or nickel-chromium plating with excellent corrosion resistance is frequently made on the surfaces of automobile cars, electrical products and parts thereof for the purpose of improving the corrosion resistance of the basic materials and improving the decorative effect by combination with decorating.
However, since flaws or cracks easily occur in the chromium surface platings obtained by such copper-nickel-chromium plating or nickel-chromium plating, corrosion is significantly progressed to the insides of the platings from the defective portions in the surfaces due to the presence of the flaws or cracks. This corrosion rapidly proceeds and finally reaches the basic materials because of the small anode area (nickel) and high corrosion current density. There is thus a great possibility that the corrosion of the basic materials brings about the occurrence of not only defects in the appearances but also fatal defects.
In order to cope with this problem, therefore, the thickness of each metal deposit is increased, or a plurality of deposits of each metal are laminated. However, such a method has a problem from the viewpoints of effective utilization of resources and cost.
The specification of Japanese Patent Publication No. 56-15471 discloses a corrosion-resistant metal film which is obtained by nickel plating using a semi-bright nickel plating and bright nickel plating solutions to each of which a brightener and a wetting agent are added, and a nickel plating solution to which a soluble amine compound and a metal selected from Groups III, V and VI in the periodic table, preferably aluminum or chromium, is added, so that fine particles are deposited on the nickel plating; and then chromium plating the nickel plating so that the local corrosion current density is decreased by the formation of micropores in the surface of the chromium plating, thereby improving the corrosion resistance.
The aforementioned prior art also has problems in that plating must be effected within a narrow control range for preventing the occurrence of dulling on the film formed after chromium plating and in that yellowing detrimental to plating occurs if the amount of the metal ions added exceeds 0.5 g/l, and such detrimental substance must be removed.